Seat belt retractor assembly

ABSTRACT

An improved seat belt retractor of the emergency locking variety is described. The primary improvement resides in providing a spur gear component which is insert molded directly onto one of the toothed sprockets of the retractor spool. By eliminating the two-piece prior art assembly, and molding the spur gear directly onto the toothed sprocket, the spur gear strength characteristics are vastly improved. Moreover, the relative positioning between the teeth of the spur gear and those of the toothed sprocket may be controlled with a very high degree of accuracy. This design further eliminates the required step of assembling the spur gear and sprocket together, and avoids problems of these components becoming separated during assembly or use.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a motor vehicle seat belt retractor andparticularly, to such a retractor having an improved inertia sensitiveactuator mechanism.

Most motor vehicles are equipped with seat belt systems which act torestrain the occupants when the vehicle is subjected to high rates ofdeceleration which may occur, for example, during a motor vehiclecollision. Many seat belt retractors are of the so-called emergencylocking variety. These retractors employ an inertia sensitive actuatorwhich prevents seat belt webbing from being withdrawn from the retractorwhen the vehicle is subjected to deceleration forces above apredetermined level, thereby restraining the vehicle occupant. Duringnormal operating circumstances, however, the seat belt webbing may befreely withdrawn from the retractor, enabling freedom of movement by thevehicle occupants.

The inertia sensitive actuator mechanism of a conventional emergencylocking retractor includes a spur gear which is attached to one of apair of toothed sprockets. These toothed sprockets are connected to arotating belt support shaft. The function of the spur gear is to engagea pawl of the inertia sensitive actuator when the vehicle is subjectedto high level deceleration. Once engaged, the inertia sensitive actuatorcauses engagement between a locking lever and the toothed sprocketthereby preventing continued seat belt webbing withdrawal from theretractor assembly. The spur gear must be accurately positioned withrespect to the toothed sprocket. Inaccurate positioning betweencomponents can lead to a mechanical failure of the spur gear and/or theremaining components of the inertia sensitive actuator. As a means ofaccurately positioning the teeth of the spur gear relative to thetoothed sprockets, it is current practice to include one or morelocating tabs on the spur gear which engage bores or indentations formedby the end surface of the toothed sprocket. It is therefore necessaryfor an operator to carefully position the parts during assembly.

In accordance with this invention, an improved seat belt retractor ofthe emergency locking variety is described. The principal improvement inthe retractor design resides in providing a spur gear component which ismolded directly to one of the toothed sprockets of the retractor. Bymolding these parts together, precise positioning therebetween can bemaintained with a high degree of accuracy. Further, the strength of thespur gear is substantially increased due to its integration with thetoothed sprocket. In addition to strengthening the spur gear itself, theconnection between the spur gear and toothed sprocket becomes much moresecure. Finally, due to the vastly increased strength and dimensionalcontrol characteristics inherent in the design according to thisinvention, a broader range of materials may be employed to form the spurgear component as compared with prior art designs.

Additional benefits and advantages of the present invention will becomeapparent to those skilled in the art to which this invention relatesfrom the subsequent description of the preferred embodiments and theappended claims, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a frontal view of a seat belt retractor of the emergencylocking variety;

FIG. 2 is a partial side view of the retractor shown by FIG. 1,particularly showing the inertia sensitive actuator of the retractor ina normal, non-engaged position;

FIG. 3 is a partial side view of the retractor shown by FIG. 1,particularly showing the inertia sensitive actuator of the retractor inan engaged position;

FIG. 4 is an exploded pictorial view of the spool and spur gearcomponents of an emergency locking retractor according to a prior artdesign;

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 1 showingan integral spur gear and toothed sprocket according to this invention;

FIG. 6 is a cross-sectinal view taken along line 6--6 of FIG. 5particularly showing the interlocking engagement between the spur gearand toothed sprocket according to this invention; and

FIG. 7 is a partial cross-sectional view taken from a direction oppositethat from which FIG. 5 is taken, thereby showing the reversed surface ofthe toothed sprocket.

DETAILED DESCRIPTION OF THE DRAWINGS

A prior art seat belt retractor is shown assembled in FIG. 1 and isgenerally designated there by reference character 10. Retractor assembly10 includes retractor frame 12 to which rotatable spool 14 is mounted.Spool 14 includes a belt support shaft 16 terminating laterally in apair of radially extending toothed sprockets 18 and 20. Tortion springassembly 22 acts upon belt support shaft 16 to rotatably bias spool 14so that a belt webbing retracting force is applied when webbing 24 iswithdrawn from retractor 10. One end of seat belt webbing 24 is attachedto belt suppport shaft 16 and becomes rolled onto spool 14 as it isrotated. Retractor frame 12 includes one or more mounting holes 26 forfasteners which permit secure attachment of retractor 10 to theassociated vehicle. Locking bar 28 is particularly shown by FIGS. 2 and3, and is movable between a normal non-engaged position to an engagedposition wherein the locking bar engages one of the teeth of toothedsprockets 18 and 20. Locking bar 28 is caused to move to an engagedposition by inertia sensitive actuator 30 which includes housing 32attached to frame 12, and internally disposed weighted element 34.Weighted element 34 moves to a tilted position once retractor assembly10 (and the associated motor vehicle) are exposed to deceleration forcesabove a predetermined level (or when retractor frame 12 is tilted fromits installed position). Once weighted element 34 is caused to move to atilted pposition, locking lever 36 becomes raised due to contact betweenthe weighted element and lug 38 of the locking lever. Locking lever 36rotates about pivot 40 between the normal and engaged positions.

FIG. 2 illustrates the normal position of the components of inertiasensitive actuator 30. When, however, weighted element 34 moves toward atilted position, locking lever 36 is caused to rotate in a clockwisedirection, with respect to the orientations shown by FIGS. 2 and 3. Onceslightly rotated, actuator pawl 42 of locking lever 36 engages a toothof spur gear 44 which is also rotatable with spool 14. Rotation of spool14 causes continued rotation of locking lever 36 until the locking levercontacts the underside of locking bar 28, urging it into engagement witha tooth of toothed sprockets 18 and 20. Actuator pawl 42 and spur gear44 are provided to augment the rotational urging forces applied tolocking lever 36 as weighted element 34 becomes tilted. Suchaugmentation results in improved reliability and accuracy of retractorlocking and provides positive engagement between locking bar 28 andtoothed sprockets 18 and 20.

FIG. 4 illustrates spool 14 and spur gear 44 according to prior artdesigns. As shown by that Figure, spur gear 44 is a separate componenttypically made from a polymeric plastic material which is connected totoothed sprocket 18 by engagement between a plurality of protrudingbosses (not shown) and holes or depressions 46 within the outer surfaceof toothed sprocket 18. The bosses and holes 46 are located such thatwhen they are in registry with one another, the teeth of toothedsprocket 18 and those of spur gear 44 are in a predetermined angularlyalingned condition. Typically, this alignment is provided by positioningbosses and holes 46 such that the two parts engage only when they are ina desired angular relationship. As is evident from a description of theoperation of the inertia sensitive actuator mechanism 30 describedabove, this precise relationship between the positions of toothedsprocket 18 and spur gear 44 must be maintained. Otherwise, excessiverotation of spur gear 44 would occur prior to engagement between lockingbar 28 and toothed sprockets 18 and 20, thereby presenting the potentialfor mechanical failure of spur gear 44 and/or actuator pawl 42.

In accordance with this invention, an integrated spur gear and toothedsprocket assembly 48 is shown with reference to FIGS. 5, 6 and 7. Thespur gear portion 50 of assembly 48 is formed by molding directly ontomodified toothed sprocket 52, as shown by cross-sectional view FIG. 6.During molding, the material which makes up spur gear 50 flows into andengages a plurality of bores or slots 54 provided through toothedsprocket 52. Enhanced reinforcement of the teeth of spur gear 50 andfirm engagement between the spur gear and toothed sprocket 52 may beprovided by forming a continuous ring 56 of material on the reverse sideof modified toothed sprocket 52 from the side having spur gear 50. Asbest shown by FIGS. 6 and 7, ring 56 communicates with each of slots 54.

Integral spur gear and toothed sprocket assembly 48 is preferably formedby first assembling the toothed sprockets onto belt support shaft 16 andthen inserting toothed sprocket 52 within an injection molding diecavity. Alternately, assembly 48 could be formed and later attached tobelt support shaft 16. Regardless of the assembly sequence, positioningmeans are provided within the mold cavity to positively locate the teethof toothed sprocket 52 with respect to the teeth of the spur gear 50.Once this location step is completed, heated polymeric plastic materialis injected under pressure within the die cavity until the materialflows to form spur gear 50. Once the material has cooled sufficiently,the assembly is removed from the injection molding die.

Integral spur gear and toothed sprocket assembly 48 provides a number ofsignificant advantages over the two-piece construction according toprior art designs as shown by FIG. 4. Since spur gear 50 is formeddirectly onto toothed sprocket 52, accurate relative positioning betweenthe teeth of these two structure is achieved. Additionally, since slots54 are provided for each of the teeth of spur gear 50, the strength ofthese individual teeth is increased significantly over the prior artspur gear 44 construction where spur gear 44 is connected to toothedsprocket 18 only by projections near the center of the spur gear. Also,due to the firm engagement between spur gear 50 and modified toothedsprocket 52, these two parts are firmly attached to each other andproblems of their becoming separated during assembly or in use areeliminated. Designers of seat belt retractors were limited to selectingmaterials for conventional spur gears which had superior dimensionalstability characteristics. This design limitation was imposed due to theexistence of some relative movement between the spur gear and sprocketand more significantly, due to deflection of the unsupported teeth ofthe spur gear as it is subjected to the broad range of environmentalconditions within a motor vehicle interior. Unfortunately, materialsselected for this application, such as Nylon, tend to be brittle andtherefore subject to mechanical failure. Due to the substantial increasein the strength of the spur gear component and the greater control overrelative positioning of components inherent in the design of integralassembly 48 according to this invention, a broader range of materialscan be employed to form the spur gear component. The material for spurgear 50 may be chosen for its low cost and formability characteristicsrather than primarily for its dimensional stability. For example,"Hytrel" (Trademark of Du Pont Company) polymeric plastic material hasbeen found suitable for use in practicing this invention. This materialis unsuitable for use in forming prior art spur gears since it ishydroscopic and tends to change dimensionally with humidity changes.Finally, by providing integral spur gear and toothed sprocket assembly48 according to this invention, manufacturing costs and steps can bereduced since the separate step of assembling the two components iseliminated.

While the above description constitutes the preferred embodiments of thepresent invention, it will be appreciated that the invention issusceptible to modification, variation and change without departing fromthe proper scope and fair meaning of the accompanying claims.

What is claimed is:
 1. In an emergency locking seat belt retractor whichprevents seat belt webbing from being withdrawn when said retractor issubjected to deceleration above a predetermined level, said retractor ofthe type having an inertia sensitive actuator with an actuator pawlengageable with a spur gear which rotates with a toothed sprocket, saidactuator pawl further engageable with a locking bar which cooperateswith said toothed sprocket to selectively inhibit withdrawal of saidseat belt webbing, the improvement comprising;a spur gear and toothedsprocket assembly wherein said toothed sprocket defines a plurality ofapertures and wherein a portion of each tooth of said spur gear isdisposed in one of said apertures whereby said spur gear is ininterlocking engagement with said toothed sprocket.
 2. The improvementaccording to claim 1 wherein the material forming said spur gear furtherforms a ring on the side of said toothed sprocket opposite the surfacefrom which said spur gear extends, said ring in communication with saidopenings.
 3. The improvement according to claim 1 wherein said spur gearis formed by Hytrel (Trademark of Du Pont Company) material.
 4. Theimprovement according to claim 1 wherein said spur gear is moldeddirectly to said toothed sprocket.